In some areas of the world (e.g. in Brazil), spark-ignited internal combustion engines are fed with different types of liquid fuel (e.g. pure petrol, hydrate alcohol, or a mixture of petrol and alcohol) which present different features (e.g. different air/fuel stoichiometric ratios). Consequently, the use of a device capable of recognising the type of fuel present in the tank in order to be able to optimise combustion control according to the type of fuel actually used was proposed for vehicles driven by spark-ignited internal combustion engines.
Currently, also modern diesel engines may use fuels other than diesel fuel which are commercially called “biodiesel” and consist of a mixture of diesel fuel and bio-mass originated fuels (e.g. vegetable oils such as rape-seed oil). However, in modern diesel engines, the engine control systems are calibrated to optimise the combustion process for diesel fuel only so as to maximise the generated mechanical power and to minimise fuel consumption and harmful emissions. Consequently, when biodiesel is used instead of diesel fuel, the engine control system calibrated to run on diesel fuel is not able to obtain an optimal combustion with a consequent considerable increase of polluting emissions (particular as concerns NOx).
From the above, it is apparent the need to define a method for recognising the fuel type in a diesel engine which is effective, efficient and inexpensive to implement in the control system of the diesel engine itself.